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Normally I don't recommend giving clients more than one assessment.  It is a bit like overload and you end up spending a heck of a lot of time on debriefing the data than getting on with the learning. 

That said, there is in my mind an excellent match for each the MBTI® and the DISC.  First, let me be VERY clear that I do not recommend using both the MBTI and DISC together.  Nine times out of ten it will only confuse the client.  They will ask you to correlate their results which is rather tricky since they  measure different things. The MBTI is a preference assessment and the DISC is a behavioural (observed) how assessment.  Second, I will assume that you are properly trained and certified in the instrument of your choice.

MBTI® and Firo-B®

Clearly, I am not the only one who thinks this is a great combination. For quite sometime the CPP in the US and Psychometrics in Canada have offered a combined MBTI® / Firo-B® Online Report.  I have always liked the Firo-B ^® and was glad to see it come back into vogue in the late 90's in leadership development programs.  It does have a strong "psych"flavour and needs to be used properly. "The Fundamental Interpersonal Relations Orientation-Behavior ™ (FIRO-B ^®)
assessment has helped people around the world unlock the mysteries of
human interaction at work and in their personal life. This instrument
quickly gathers critical insights into how an individual's needs for
inclusion, control, and affection can shape his or her interactions
with others."  Here's what they say on the web site:

Leadership Report Using FIRO-B ^® and MBTI ^® Instrument 17 pages

The
FIRO-B and MBTI instruments tap into key aspects of personality and
behavior in areas such as communication, problem solving, decision
making, and interpersonal relations. The instruments are also quite
distinct, each providing a view through a different window of the
client's leadership personality. Together, they complement each other
and provide rich information of use in a personal, ongoing leadership
development program.

DISC and Values (Spranger and Allport's Motivators)

I knew of two different vendors offering this combination and I am now pleased to report that their is a third one on  the market.  All of them are based on the research of Dr. Eduard Spranger and Gordon Allport who looked into what drives and
motivates an individual. The seven dimensions of value discovered between these two researchers help map the reasons that drive an individual to utilize their talents in the unique way they do. These assessment helps clients understand  motivators and drivers and how to maximize  performance by achieving better alignment and
passion for what they do.

The three that I know of are:

1. The PIA&V (Personal Interests, Attitudes and Values™ from TTI Performance Systems.
   TTI along with Inscape is a recognized source for solid
   DISC instruments in the personal and business coaching communities and is also
   the distributor of PIAV which
   is a nice companion tool with the DISC.

2. The founder of Maximum Potential co-created the PIAV with Bill
   Bonnstetter of TTI. He has the rights to a similar product.  Maximum Potential uses more business language but unlike the PIAV, it does
   not have normative data.
   

3. My new portal Assess Yourself will be offerning the Online Assessments from Tony Alessandra. The Online Values Assessment measures seven dimensions of motivation (and similar to those above) as outlined below:

• Aesthetic – a drive for balance, harmony and form.
• Economic – a drive for economic or practical returns.
• Individualistic – a drive to stand out as independent and unique.
• Political – a drive to be in control or have influence.
• Altruistic – a drive for humanitarian efforts; help others altruistically.
• Regulatory – a drive to establish order, routine and structure.
• Theoretical – a drive for knowledge, learning and understanding.